中文XML论坛--C#快餐

发信人: walts (休息一会), 信区: DotNET
标  题: C#快餐－3
发信站: BBS 水木清华站 (Thu Jul 26 01:14:38 2001)

  Lesson 3. Hacker's introduction to MSIL Part2.

   Let's recall garbage collection rules that we have learned in Lesson2
   No data or local variables can be left on stack when program terminates.
add adds data and the variable on top of the stack. The data is popped
from the stack, and the result is stored inside the variable, which remains
on stack.
  Function calls such as Console::WriteLine(...) print and pop a variable
from the stack. They cannot print data directly.. Garbage collection of
variables which are not stored on the stack is automatic.
   Before we look at a much more interesting example of OO programing,
let's learn how to pass parameters to a function. The simplest example.
.assembly hello{}
.class Test{
    .method private static void hello(int32) il managed
    {
        ldarg.0
        call void [mscorlib]System.Console::WriteLine(int32)
        ret
    }
    .method public static void Main() il managed
    {
        .entrypoint
        ldc.i4.3
        call void Test::hello(int32)
        ret
    }
}
     Note the use of keyword ldarg.0 to load an integer argument of void hel
lo(int).
This argument is then  stored on the stack and is later  passed to WriteLine
.
     Let's look at a more interesting C# example involving creation of a cla
ss.
using System;
class mInt
{
    public int x=3;
}
class Test{
    public static void Main(){
    mInt mint=new mInt();
    Console.WriteLine(mint.x);
    }
}
This program translates into the following MSIL code:
.assembly hello{}
.class mInt {
    .field public int32 x
    .method public instance void .ctor() il managed
    {
        ldarg.0 //null argument needs to be passed to the constructor or
        //InvalidProgramExecution exception is thrown
        ldc.i4.3
        stfld int32 mInt::x
        ret
    }
}
.class Test
{
    .method static public void main(){
        .entrypoint
        newobj instance void mInt::.ctor()
        //create a new instance of mInt on the heap
        ldfld int32 mInt::x
        call void [mscorlib]System.Console::WriteLine(int32)
    ret
    }
}
     .method public instance void .ctor() il managed declares a constructor
of
class mInt. As we  learned in our first OO class, the compiler is providing

a default constructor if we have not written one yourself. When programming

MSIL we are doing some of the compiler work.
So, welcome to .ctor() notation! .ctor() is responsible for
explicit initialization of all data members of class mInt.
The declaration of int x is done with .field keyword.
The .ctor() is loading data into mInt fields with with a call stfld.
All constructors are designated with .ctor keyword.  newobj is MSIL's
  equivalen of new. Usually constructors return void.
  The syntax of MSIL seem to allow non void constructors.
  Let's first look at a simpler problem of returning by value in MSIL.
ldfld field Push on the stack field of an object
newobj ctor Create a new instance of the object,  initialize its
fields to 0 or null and  push it on the stack
stfld field Replace the value of a  field of an object
ldarg Load first argument of the method into the stack
The program below shows how to return a value. The value is simply
left on the stack in a local variable of mtest(). When mtest() is called,
the local variable of mtest() is transferred to a local variable of Main,
  which in turn is pushed on stack of Main.
.assembly hello{}
.class Test{
.method private static int32 mtest() il managed
{
.locals (int32 V_0)
ldc.i4.3
stloc.0
ldloc.0 //push variable on stack
ret
}
.method public static void Main() il managed
{
.entrypoint
call int32 Test::mtest()
call void [mscorlib]System.Console::WriteLine(int32)
ret
}
}
Exercises
    1. Which identifiers are not allowed in C#: $Test, ?hi, @weird,_down.?
    2. Find a mistake in this page.
    3. Write a really cool program and send it to me. Do not forget to
    put a lot of comments.

--

A great poem is a fountain forever overflowing with the
　waters of wisdom and delight.
　　　　　　　　　　　
                                          —— Shelley

※ 来源:·BBS 水木清华站 smth.org·[FROM: 166.111.142.118]
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